Calculation of ground water ages--a comparative analysis

Area of Science:

• Hydrogeology
• Environmental Modeling
• Isotope Hydrology

Background:

• Groundwater age is crucial for understanding aquifer dynamics.
• Discrepancies exist between different groundwater age modeling approaches, particularly advection-based versus direct simulation (age-mass) methods.
• The influence of advection and dispersion on modeled ages requires further investigation.

Purpose of the Study:

• To assess the impact of advection and dispersion on modeled 14C and directly simulated groundwater ages.
• To compare the reliability of different groundwater age modeling approaches in various hydrogeological settings.

Main Methods:

• Utilized two-dimensional (2D) simulations to model groundwater flow and age.
• Assessed the effects of longitudinal and vertical dispersion on 14C and directly simulated ages.
• Investigated the influence of permeable and impermeable faults on age discrepancies.

Main Results:

• Dispersion has a stronger impact on modeled ages in low-velocity zones and significantly affects 14C ages.
• Longitudinal dispersion acts as a 14C source, while vertical dispersion acts as a sink, causing apparent age variations.
• Faults introduce substantial discrepancies between the three modeling methods.

Conclusions:

• The 14C solute transport modeling approach is more reliable in simpler systems (high velocity, no faults).
• Direct simulation of groundwater age provides the most consistent results in complex, heterogeneous systems.
• Direct simulation aligns better with expected age structures based on flow system dynamics.